Terephthalonitrile purfication process

ABSTRACT

A PROCESS FOR THE SEPARATION OF BENZIONITRILE AND P-TOLUONITRILE FROM ADMIXTURE WITH TEREPHTHALONITRILE BY SUBJECTING SAID MIXTURE TO EXTRACTION WITH ACETONITRILE, FIRST AT A TEMPERATURE FROM ABOUT -20*C. TO ABOUT 10*C. WHEREBY BENZONITRILE IS REMOVED, AND THEN TO A SECOND EXTRACTION AT A TEMPERATURE FROM ABOUT 30*C. TO ABOUT 80*C. WHEREBY P-TOLUONITRILE IS REMOVED.

Nov. 6, 1973 R. v. NORTON TEREPHTHALGNITRILE PURIFICATON PROCESS Filed Feb. 22, 1972 QB lNN United States Patent Oliice 3,770,800 Patented Nov. 6, 1973 3,770,800 TEREPHTHALONITRILE PURIFICATION PROCESS Richard V. Norton, Wilmington, Del., assignor to Sun Research and Development Co., Philadelphia, Pa. Filed Feb. 22, 1972, Ser. No. 228,160 Int. Cl. C07c 121/52, 121/58 U.S. Cl. 260-465 C 4 Claims ABSTRACT OF THE DISCLOSURE Terephthalonitrile is an intermediate to terephthalic acid which is an important chemical of commerce in its use for the preparation of polyethyleneterephthalate fibers. Terephthalonitrile may be prepared by the vapor phase ammoxidation of p-xylene and when so prepared contains p-toluonitrile as a major impurity and benzonitrile in minor amounts. Both of these impurities must be removed prior to the conversion of the nitrile to terephthalic acid.

In the usual practice heretofore as disclosed by U.S. Pat. 2,846,462 (Hadley, D. S. assigned to Distillers Co., Ltd., issued Aug. 5, 1958) the gases from the ammoxidation reactor are cooled to deposit the mixture of nitriles as a solid and the toluonitriles are removed by extraction with paraffinic solvents such as petroleum ether, or alternatively, the mixture is purified by distillation methods. It has now been found, however, that a very simple extraction process with acetonitrile operated over two distinct temperature ranges provides a highly eticient process for purification of terephthalontrile whereby both benzonitrile and p-toluonitrile impurities are removed.

In accord with the invention, benzonitrile and p-toluonitrile are separated from admixture with terephthalonitrile or p-toluonitrile. It will also be understood that the process is readily carried out in conventional extractions, is simply mixed thoroughly with the liquid acetozonitrile extraction step of the process the preferred ternperature will be in the range of about 0 to about 5 C. and for the p-toluonitrile extraction the preferred temperature will be from about to about 60 C.

Another embodiment of the invention includes a continuous process in that after each of the extraction steps the acetonitrile extractant is distilled off and recycled for reuse. Likewise, the p-toluonitrile extracted in the second step may be separated from the acetonitrile and recycled to the ammoxidation unit for conversion to terephthalonitrile. It will, of course, be understood that should color bodies form and/or build up during recycle, they are readily removed by treatment of the liquid with activated charcoal.

This invention will be of greatest value in separating the products from ammoxidation with a non-selective catalyst; c g., the product composition may contain as much as p-toluonitrile and up to about 10% benzonitrile. However, the process is of significant value with arnmoxidation product mixtures containing 20% p-toluonitrile and less than 0.1% benzonitrile, which together with terephthalonitrile is the product from a selective ammoxidation. Preferably, for use in the process of the invention, an ammoxidation product will be used which contains from about 20% to about 50% p-toluonitrile, from about 0.01 to about 3% benzonitrile, and the balance being terephthalonitrile.

In order to further illustrate the invention, the following examples are given:

EXAMPLES l TO 5 Terephthalonitrile (TPN) containing various amounts of benzonitrile (BN) and p-toluonitrile (TN) are extracted with acetonitrile at various temperatures in accord with the invention and the extracted solid and filtrate is analyzed. For each extraction 15.6 parts by weight of acetonitrile is used for S parts of TPN. The data and results obtained are shown in the following Table I:

TABLE I First extraction Second extraction Mixture composition Lq- (WR Cryst. Li wt. (wt, percent) Cryst. (wt. percent) percent) (wt. percent) peticnt) Example em emp., No. TPN TN BN C. TPN TN BN BN TN C. TPN TN TN TPN 60 35 5 3 62. 5 36. 8 0. 7 99. 8 0. 2 60 96. 7 3. 3 95 5 7o 25 5 7 73. 0 26. 2 o. 8 99. s o. 2 55 97. 2. 4 96 4 80 15 5 0 83. 6 15. 7 0. 7 99. 9 0. 1 60 98. 8 l. 2 94 6 12 3 6 85. 2 12. 3 0. 5 99. 9 0. 1 55 99. 5 0. 5 93 7 9 1 5 90. 9 9. 1 0. 99. 9 0. 1 50 99. 9 0. 1 95 5 nitrile by subjecting said mixture to extraction with acetonitrile, iirst at a temperature of from about -20 C. to about 10 C. to remove benzonitrile, and then at a temperature of from about 30 C. to about 80 C. to remove p-toluonitrile.

Another object of the invention is to provide a continuous process whereby the extractant acetonitrile and recovered p-toluonitrile is recycled thereby providing a highly efiicient low cost operation.

In carrying out the process of the invention, the terephthalonitrile, which is solid under the extraction conditions, is simply mixed thoroughly with the liquid acetonitrile at the desired treatment temperature and the mass ltered. Generally, for each extraction, the weight ratio of liquid acetonitrile to terephthalonitrile will be from about 2:1 to about 15:1, the preferred ratio being about 3:1. However, the amount of acetonitrile used is in no way critical to the process; the amount to be used will simply be sufficient to effect suitable extraction of the benzo- As can be seen from the above data, the first extraction was quite effective in carrying benzonitrile into the liltrate, thus removing it from the terephthalonitrile. In the second extraction, the p-toluonitrile is likewise removed, yielding a highly purified terephthalonitrile product.

EXAMPLE r6 A continuous extraction is carried out in accord with the process details set forth in the drawing. As shown there, the products of an ammoxidation reaction containing terephthalonitrile, benzonitrile, and p-toluonitrile are taken through line 10 to a continuous solid-liquid extraction unit A operated at 10" C. to 0 C. to which acetonitrile is added through line 11. The extracted solid is taken through line 12 to a vacuum filter B, the solid then going through line 13 to a second continuous solid-liquid extraction unit C operated at 55 to 60 C., and to which acetonitrile is added through line 14. The extracted solid is taken through line 1S to a vacuum filter D and the solid taken off at line 16 is essentially pure terephthalonitrile. The liquid acetonitrile containing extracted components from the first extraction is taken through line 17, is comb-ined through line 18 with the ltrate from the vacuum filter B and is taken through line 19 to a distillation tower E. Fractional distillation removes acetonitrile overhead at 82 C., taken through line 20 for recovery and/or recycle at line 11 and/or 14. 1n the same tower E benzonitrile is recovered at 190 C. through line 21 and the bottoms flowing through line 22 at 220 to 250 C. are essentially pure terephthalonitrile which may be combined with that taken from line 16. The acetonitrile from the second extraction is taken through line 23, combined with the tiltrate from the vacuum filter D in line 24 and the combined liquid fed through line 25 to a distillation tower F. Here acetonitrile taken as overhead at 82 C. is recovered through line 26 and recycled through line 11 and/ or 14 to an extraction unit. Para-toluonitrile is recovered at 217 C. through line 27 and is recycled to the ammoxidationreactor for conversion to terephthalonitrile. 'The bottoms comprise essentially pure terephthalonitrile which is taken off through line 28.

Table II which follows gives numerical data for the flow lines shown in the gure for the above described process.

TABLE I1 Lbs/hr.

Aceto- Line "I'PN TN BN nitrile 80. 15. 0 5. 0 0 0. 0 0. 0 0. 0 100 78. 1 14. 1 0. 2 5 78. 1 14. 0 0. 1 0 0. 0 0. 0 0. 0 400 76. 0.9 0. 0 6 T6. 3 0. 3 0. 0 0 1. 9 0. 9 4. 8 395 0. 0 0. 1 0. 1 5 1. 9 1. 0 4. 9 400 0. 0 0. 0 0. 0 400 O. 0 0. 9 4. 0 0 l. 9 0. 1 0. 0 0 1. 6 13. 1 0. 1 304 0. 0 0. 6 0. 0 6 1. 6 13. 7 0. 1 400 0. 0 0. 0 (lV 0 400 0. 0 13. 5 0. 1 0 1. 6 0. 2 0. 0 0

The invention claimed is:

l. A process for the separation of benzonitrile and ptoluonitrile from admixture with terephthalonitrile obtained by vthe amrnoxidation of p-xylene by subjecting said mixture of terephthalonitrile containing up to p-toluonitrile and up to about 10% benzonitrile to extraction with aceftonitrile in an amount corresponding to a weight ratio of acetonitrile to terephthalonitrile of from about 2:1 to 15:1, first at a temperature form about 20" C. to about 10 C. whereby benzonitrile is removed, and then to a second extraction at a temperature from about 30 C. -to about 80 C. whereby p-toluonitrile is removed.

2. The process of claim 1 Where the first extraction is at a temperature of from about 0 to about 5 C. and the second extraction is at a temperature of from about 50 to about 60 C.

3. A process for the purication of terephthalonitrile obtained by the ammoxidation of p-xylene which comprises subjecting a mixture of terephthalonitrile containing from about 20% to about 50% p-toluonitrile and from about 0.01 to about 3% benzonitrile to a rst extraction with acetonitrile in an amount corresponding to a weight ratio of acetonitrile to terephthalonitrile of from about 2:1 to 15:1 at a temperature from about -20 to about 10 C. whereby benzonitrile is removed, subjecting the extracted lterephthalonitrile to a second acetonitriie extraction at a temperature of from about 30 C. to about C. whereby p-toluonitrile is removed, separating ptoluonitrile and acetonitrile from the liquid extractant, recycling said p-toluonitrile to said amrnoxidation reaction and recycling acetonitrile for reuse for extraction of terephthalonitrile.

4. The process of claim 3 where the rst extraction is carried out at about 0 to about 5 C. and the second extraction is carried out at about 50 to about 60 C.

References Cited UNITED STATES PATENTS 2,846,462 8/1958 Hadley 260-465 C 3,135,795 6/1964 Gasson et al 260-465 C 3,362,982 1/1968 Oga et al. 260-465 C 3,468,763 9/1969 Paguch 260-465 H X JOSEPH P. BRUST, Primary Examiner 

